Arsenic removal from aqueous media using chemically treated zeolite materials

ABSTRACT

Systems and methods are provided for the removal and disposal of arsenic from an aqueous medium. The systems and methods include the removal of arsenic from a source by contact with either a chemically treated natural or synthetic zeolite, for example a ferric-loaded zeolite. The spent zeolite is disposed of at an appropriate arsenic disposal site. A system for monitoring and maintaining an arsenic removal/disposal system by an off-site provider is also disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

The present non-provisional patent application claims priority to U.S.Provisional Application Ser. No. 60/325,265, filed on Sep. 26, 2001,entitled TRACE ELEMENT REMOVAL FROM AQUEOUS MEDIA USING CHEMICALLYTREATED ZEOLITE MATERIALS, which is incorporated herein by reference.

FIELD OF THE INVENTION

The invention generally relates to the removal of arsenic from aqueousmedia. More specifically, the invention provides systems and methods forcost effectively removing arsenic from water as it is treated in a watertreatment facility, and in particular, to systems and methods for theremoval and disposal of arsenic from drinking water by contacting thewater with chemically treated zeolite materials before or after thewater has been purified in a water treatment facility.

BACKGROUND OF THE INVENTION

Cities and towns throughout the world depend on having clean potablewater supplies. The dependence on clean water has increased as thepopulation of the world has increased, especially as industrial use ofrivers and lakes have become commonplace.

The explosion of world population, and corresponding increase in freshwater use, has, therefore, resulted in a need to maximize water usage.However, the ability to maximize fresh water use has been limited by,(1) increased pollution of the fresh water supplies due to higherindustrial output throughout the world (a direct result of the increasedpopulation); and (2) increased knowledge and standards for whatconstitutes clean water, acceptable for use in farming, industry, andconsumption. As a result, there is a current need to increase theefficiency in the use of water, i.e., conserve existing clean watersupplies, increase the current capabilities used to remove pollutantsfrom water supplies, and increase the effectiveness of existing and newtechnologies to effectively treat and reach new standards in waterquality.

In this light, arsenic, a soluble element that occurs naturally, hasbecome of concern to the water supplies of many population centersthroughout the world, and in particular, portions of the world where theelement is found in high concentrations, e.g., Bangladesh, NorthernChile, etc. Of particular importance to these areas of high arsenicconcentration, and to other lower arsenic concentration areas as well,is the fact that arsenic has been found to be a toxin and carcinogen andaccumulates within tissues over a period of time.

The drinking water standard for arsenic, set in the 1940's, wasoriginally 50 parts per billion (ppb). Over the last several decades,the Environmental Protection Agency (EPA) and academia have beenstudying the potential health effects of arsenic intake, and inparticular have focused on the health effects of arsenic in and aroundthe EPA set level of 50 ppb. For example, at arsenic levels of around100 ppb there appear to be potential serious health effects on humans,such as increased potential of certain cancers and a weakened immunesystem. However, at arsenic levels closer to 50 ppb and lower, thestudies show conflicting results as to arsenic's effects on health,suggesting that additional studies are needed to clarify what level ofarsenic is appropriate for long term consumption in drinking water.

In the 1990's the EPA recommended that the arsenic limit in drinkingwater be lowered to 10 ppb. No action was taken on the EPA's proposaluntil days before the Clinton administration was scheduled to leaveoffice, at which time President Clinton approved of arsenic levels beinglowered from 50 ppb to 10 ppb. In addition, wide spread support forfurther lowering the standard to 5 ppb arsenic has gained acceptancewithin a number of environmental groups. There are a significant numberof drinking water facilities that would violate an arsenic standardlower than the 50 ppb standard. In particular, over 3,500 drinking waterfacilities in at least 24 states would violate a 5 ppb arsenic standard,illustrating the need for utilizing some type of arsenic removal systemin at least these facilities.

Currently, commercial scale removal of arsenic is accomplished usinggranulated ferric oxide and activated alumina, or to a lesser extent, byusing ferric hydroxide. Although theoretically effective at arsenicremoval, these techniques are costly, tending to run in the range of$1,200/ton for the activated alumina or for the ferric hydroxide,thereby making their use less attractive. Additionally, granular ferrichydroxide has proven to be friable, adding to the cost of using thecompound, and activated alumina has proven to have a higher affinity forfluorine than arsenic, making high fluorine water sources unacceptabletargets for the activated alumina technique. As such, there is a need inthe industry for providing an arsenic removal system that overcomesthese current deficiencies in arsenic removal, and has the ability tosufficiently treat water supplies and reach the proposed MCL forarsenic, whether it be 10 ppb or 5 ppb. Ideally these new arsenicremoval techniques are cost effective and useful in high fluorinecontaining water supplies. Against this backdrop the present inventionhas been developed.

BRIEF SUMMARY OF THE INVENTION

The present invention provides systems and methods for the removal ofarsenic from an aqueous medium using the exchange properties ofchemically treated zeolite materials. The chemically treated zeolites ofthe present invention absorb arsenic at levels sufficient to comply withthe current MCL for drinking water, as promulgated by the EnvironmentalProtection Agency. Spent zeolites are replaced and disposed of atarsenic approved landfills. Preferably, the chemically treated zeoliteshave ferric iron absorbed at a sufficient level to provide a higharsenic capacity zeolite material for use in removing arsenic from watersources throughout the United States and world.

The present invention also provides a system for operating an arsenicremoval facility, in accordance with the present invention, from anoff-site location. The system includes providing a pre-determined amountof chemically treated zeolite for removal of arsenic from the targetwater source, monitoring the feed and discharge of the target watersource for arsenic levels, modifying the capacity of the chemicallytreated zeolite to remove arsenic from the feed by replacing an amountof spent chemically treated zeolite with fresh chemically treatedzeolite when appropriate amounts of bed volumes, time or dischargereadings have been attained, and disposing of the spent zeolite in anarsenic approved landfill. Typically, the operating of the arsenicremoval facility is performed at a water treatment facility.

These and various other features as well as advantages whichcharacterize the invention will be apparent from a reading of thefollowing detailed description and a review of the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a flow diagram of a method for removing arsenic froman aqueous media in accordance with an embodiment of the presentinvention.

FIG. 2 illustrates a flow diagram of a method for removing arsenic froman aqueous media in accordance with another embodiment of the presentinvention.

FIG. 3 illustrates a schematic for removing arsenic from an aqueousmedia in accordance with an embodiment of the present invention.

FIGS. 4A and B illustrate schematic for removing arsenic from an aqueousmedia in accordance with another embodiment of the present invention.

FIG. 5 illustrates a schematic for removing arsenic from an aqueousmedia in accordance with another embodiment of the present invention.

FIG. 6 is a tabular and graphical representation of ferric iron loadingon zeolite in accordance with an embodiment of the present invention.

FIGS. 7A-C are tabular (7A & 7B) and graphical (7C) representations ofthe feed and discharge arsenic levels in a water source as the watersource is circulated over the chemically treated zeolite of the presentinvention for a number of bed volumes.

FIGS. 8A & 8B illustrate arsenate removal from an aqueous medium inaccordance with one embodiment of the present invention

FIGS. 9A & 9B illustrate pilot study data for removal of arsenic fromaqueous medium in accordance with one embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Definitions

The following definitions are provided to facilitate understanding ofcertain terms used frequently herein and are not meant to limit thescope of the present disclosure.

“Aqueous medium” refers to water or any liquid made from, with, or bywater.

“Feed” refers to an aqueous medium before treatment with the systems andmethods of the present invention, for example, a flowing water sourcebefore it enters a water treatment facility.

“Arsenic” or “As” refers to, in general, a nonmetallic element of atomicnumber 33, having valences of 2, 3, and 5. Arsenic is a known carcinogenand mutagen. For purposes of the present invention, the term arsenicincludes arsenate (AsO₄) and arsenite (AsO₃).

“Maximum Contaminant Level” is the highest level of contamination thatis allowed in drinking water in the United States, taking into accountbest treatment technology and cost. These standards are typicallyenforceable. Note that Maximum Contaminant Level standards areenvisioned to encompass or correspond to the same approximate standardsin countries outside the United States, and in may cases are enforceablein those countries. The MCL for arsenic in the United States is 10 ppb.

“Zeolite” refers to a natural and/or synthetic zeolite. Natural zeolitesare hydrated silicates of aluminum and either sodium or calcium or both,for example clinoptilolite and chabazite. Synthetic zeolites are made bya number of well known processes, for example gel or clay processes,which form a matrix to which the zeolite is added. Example syntheticzeolites include Linde® AW-30 and Zeolon® 900.

“Approved landfill” refers to any governmentally approved arsenic wastehandling facility.

“arsenic measuring device” refers to any detection device having thecapacity to detect the level of arsenic in an aqueous medium, forexample, Inductively Coupled Plasma spectroscopy (ICP).

“bed volume” for a particular housing member refers to the volume ofchemically treated zeolite in the housing member. The term bed volume,for purposes of the present invention, also refers to the retentionvolume and/or specific retention volume. Note that bed volume has unitsof liters, cubic meters, or cubic feet.

“Remove” refers to the detectable decrease of a target material, forexample arsenic, from a source, for example ground water. Typicallyremoval of arsenic from an aqueous source is at least 50%, preferably atleast 75% and most preferably at least 90%, from the original levels inthe zeolite treated source.

“Absorb” and “adsorb” refer to the same basic principle of one substancebeing retained by another substance. The processes can includeattraction of one substance to the surface of another substance or thepenetration of one substance into the inner structure of anothersubstance. The present invention contemplates that chemically treatedzeolite can either absorb and/or adsorb arsenic out of an aqueous mediumand that for purposes of the present invention, that the two principlesbe interchangeable. Other terms used to describe this interactioninclude binding or trapping, each of which contemplate absorption and/oradsorption.

Generation of Chemically Treated Zeolites

In preferred embodiments of the present invention, a chemically treatedzeolite is provided for removal of arsenic from an aqueous medium.

Zeolites:

Compositionally, zeolites are similar to clay minerals, where zeolitesare natural hydrated silicates of aluminum and either sodium or calciumor both. Unlike clays, which have a layered crystalline structure(similar to a deck of cards that is subject to shrinking and swelling aswater is absorbed), zeolites have a rigid three-dimensional crystallinestructure. Zeolites' rigid honeycomb-like crystalline structure consistsof a network of interconnected tunnels and cages, thereby forming aseries of substantially uniformly sized pores. Aqueous media movesfreely in and out of the pores formed by the crystalline structure,making zeolite an excellent sieving or filtration type material, as wellas providing a large surface area for binding target ions. Zeolite ishost to water molecules and ions or potassium, sodium, and calcium, aswell as a variety of other positively charged ions, but only those ofappropriate molecular size fit into the pores, creating the “sieving”property.

There are approximately fifty different types of natural zeolites,including clinoptilolite, chabazite, phillipsite, mordenite, analcite,heulandite, stilbite, thomosonite, brewsterite, wellsite, harmotome,leonhardite, eschellite, erionite, epidesmine, and the like. Differencesbetween the different zeolites include particle density, cationselectivity, molecular pore size, and cation affinity. For example,clinoptilolite, the most common natural zeolite, has 16% more voidvolume and pores as much as 0.2 nm larger than analcime, another commonzeolite.

Zeolites having particle sizes from 10×60 mesh, and preferably 20×40mesh are useful in the present invention, although slightly larger andsmaller sized zeolite can be used, just less effectively. Zeolite finesare typically removed before use in the present invention to preventplugging in the tanks of the present invention (see below). Preferablenatural zeolites for use in the present invention includeclinoptilolite.

Tables 1 and 2 provide a list of companies that presently producezeolite minerals in either the United States or Canada. Table 1 providesa chemical analysis of the zeolite materials by company, and Table 2provides the physical properties of the corresponding zeolite materialsfor each company. These Tables are provided as illustrative of the typesof zeolite material that can be purchased for large scale use in thepreparation of chemically treated zeolite.

TABLE 1 Chemical Analysis (Expressed in Weight %) Company Location Na₂OK₂O CaO MgO SiO₂ Al₂O₃ TiO₂ Fe₂O₃ Addwest WY 4.7 1.9 1.6 0.65 74.0 14.00.1 2.1 Minerals American NV/CA 3.5 3.8 0.7 0.4 69.1 11.9 — 0.74Research Am. OR 0.8 3.8 0.7 0.4 69.1 11.9 0.2 0.7 Absorbents StellheadCA/NM/OR 0.8 3.8 0.7 0.4 69.1 11.9 0.2 0.4 Res. Teague OR 0.9 4.7 1.40.3 64.1 11.8 0.3 2.58 Minerals Zeotech TX 0.6 1.7 2.4 0.7 68.4 12.1 NKNK St. Cloud NM 0.9 3.3 3.3 1.0 64.7 12.6 0.2 1.8 Mining W-Way Canada2.5 2.7 3.4 1.3 65.8 14.3 0.3 2.6 Zeolites Highwood Canada 2.78 2.793.78 0.95 64.5 13.7 0.27 2.19 Res C2C Canada 1.35 1.57 2.51 1.55 66.811.2 0.6 5.2 Mining Mining

TABLE 2 Physical Properties Ionic Exch Capacity H₂O % Free Pore Company(meq/g) Adsorp Silica (%) SG Color pH Diam. (Å) Hard Addwest 2.00 14.02.00 1.5 pale 4.4 3.7 Minerals blue American 1.85 12.3 NK NK 4.0 5.1Research Am. 1.4 1.50 2.3 white 8.0 4.0 3.8 Absorbents Stellhead 1.300.09 1.6 white 8.0 4.0 5.1 Res. Teague 1.77 low 2.2 off not not Mineralswhite provided pro- vided Zeotech St. Cloud 1.60 0.01< 2.3 white 8.0 4.03.8 Mining W-Way 1.00 25.0 NK 2.4 off 8.1 6.5 NK Zeolites white/ palegreen Highwood 1.00 10.0 2.0 7.0 Res C2C NK NK 5.00 2.3 brown 5.0? NK NKMining

It is also envisioned that synthetic zeolites can be used in accordancewith the present invention. Synthetic zeolites are made by well knownprocesses, such as a gel process (sodium silicate and alumina) or clayprocess (kaolin), which form a matrix to which the zeolite is added.Preferable synthetic zeolites include Linde®AW-30, Linde®AW-500,Linde®4-A and Zeolon®900.

It is envisioned that the systems and methods of the present inventioncan utilize either natural, synthetic or a mixture of natural andsynthetic zeolite in the preparation of the chemically treated zeolite.

Chemically Treated Zeolites:

The zeolites used in the present invention include any zeolite having acapacity for loading ferric ions, and other similarly reactive metalions, to a sufficient capacity for use in the removal of arsenic from anaqueous medium. The chemically treated zeolites of the present inventionact both as molecular sieves and as affinity exchange medium for theremoval of arsenic from an aqueous medium.

In general, the chemically treated zeolites of the present invention areprepared using the following process: the fines and clays are removedfrom the zeolite material, typically by decanting or using commercialscrubbing and sizing devices such as trommels, classifiers, andvibrating screens. To illustrate the remainder of the process aferric-loaded zeolite is described, although other chemically treatedzeolites are contemplated to be within the scope of the presentinvention. A ferric containing solution is added to the zeolite, forexample ferric sulfate, to provide from about 0.5 to 4 meq of ferriciron per gram of zeolite. The ferric iron is allowed tocontact/circulate over the zeolite for a pre-set amount of time or bedvolumes. The pH of the reaction is controlled to minimize precipitationof the various iron containing materials, preferable pH conditions arefrom about 2.0 to 2.5, although a pH of slightly above or below thisrange is envisioned to be within the scope of the present invention.

Once the zeolite is loaded with ferric ions, the chemically treatedzeolite is slowly rinsed and neutralized to remove the unbound ions andto raise the pH of the column to a range of from 4.0 to 5.5. The pHchange must occur slowly with regard to the zeolite to avoidprecipitation of the iron out of solution. A number of differenthydroxides are useful in raising the pH, for example sodium hydroxideand calcium hydroxide.

The column can then be drained, dewatered, and low-temperature dried.Although ferric ions are preferable for loading onto the zeolites of thepresent invention, other like metallic ions can be substituted. Thechemically treated zeolite materials for use in the present inventioninclude: ferric-loaded zeolite, ferric hydroxide-loaded zeolite,aluminum-loaded zeolite, barium-loaded zeolite, zinc-loaded zeolite andcopper-loaded zeolite. Further, it is recognized that each of thedifferent chemically treated zeolites has a different affinity forvarious forms of arsenic. For example, the ferric-loaded zeolite ishighly effective in absorbing arsenic in the form of arsenate, but lesseffective at absorbing arsenite, and, in contrast, aluminum-loadedzeolites are more effective at absorbing arsenic in the form ofarsenite.

Table 3 illustrates examples for the preparation of ferric-loaded andaluminum loaded zeolite.

TABLE 1 Preparation Of Ferric-Loaded And Aluminum Loaded ZeolitePurpose: Wash, screen, and metal-load zeolite for use in tests arsenicremoval Procedure: Pulp 500 grams zeolite in hot water for 30 minutes.Settle, decant Repulp in hot water for 5 minutes Settle, decant Screenon 35 or 40 mesh screen to remove fines. Low-temperature (50° C.) ovendry When dry, rescreen on 35-40 mesh screen. Ferric form zeolite: Take200 grams of dry, sieved zeolite Contact overnight with 37.6 gramsFe2(SO4)3.xH20 404.0 meq Fe in 2000 ml water. Sieved solutions torecover zeolite and rinse zeolite with water. Measure solution/washvolume 2180 ml Measure solution final pH 2.05 Submit for iron analysisWRT-5-22-1 Air dry zeolite WRT-5-22-2 Aluminum form zeolite: Take 200grams of dry, sieved zeolite Contact overnight with 44.4 gramsA12(SO4)3.18H2O 400.0 meq Al in 2000 ml water. Sieved solutions torecover zeolite and rinse zeolite with water. Measure solution/washvolume 2200 ml Measure solution final pH 2.30 Submit for aluminumanalysis WRT-5-22-3 Air dry zeolite WRT-5-22-4 meq residual Analyses AlFe Ca Na Al Fe FeZ 1755 125 905 206 AlZ 1355 26 595 331 Loading onzeolite, Meq/g Fe Al Ca Na Iron 0.99 0.034 0.429 Aluminum 0.34 0.0140.285

In general, the chemically treated zeolites are preferably prepared byprocesses that keep more of the surface area of the zeolite materialopen for absorption. Processes, such as precipitation of the ions ontothe zeolite, are less desirable for chemically treating zeolite as theprecipitated ions may seal the zeolite pores, thereby decreasing thesurface area to absorb arsenic. As such, pH values above the metallicions precipitation value, during the production of chemically treatedzeolites, are avoided.

Note that various combinations of chemically treated zeolites can beutilized in one or more housing members to maximize the capacity of thechemically treated zeolite for removal of all species of arsenic fromthe aqueous medium. For example, one housing member may be loaded with amixture of ferric-loaded zeolite and aluminum-loaded zeolite, or anaqueous medium could be run through a first housing member charged witha ferric-loaded zeolite and then through a second housing member chargedwith a aluminum-loaded zeolite. The combinations of loaded-zeolites canbe selected depending on the characteristics of the particular aqueousmedium and the species of arsenic contained therein. The proportions ofthe various loaded-zeolites can also be varied accordingly. Thisprovides broad latitude to custom design arsenic removal systems andmethods for a variety of aqueous medium.

Arsenic Removal From Aqueous Medium Using Chemically Treated Zeolite

The present invention relates to systems and methods for extractingarsenic present in an aqueous medium at a first level to arsenic presentin an aqueous medium at a second, third, etc, level. For purposes of thepresent invention, a “first level” of arsenic is preferably aconcentration within an aqueous medium that exceeds the acceptabledischarge limits, or Maximum Contaminant Levels (MCL), set by theEnvironmental Protection Agency (EPA) measured in parts per billion(ppb), i.e., 10 ppb. Note that for purposes of the present invention,MCL is envisioned to incorporate or corresponds to the regulatoryarsenic limits set by other countries besides the United States, and EPAis envisioned to represent not only the regulatory authority of theUnited States, but to represent regulatory authorities in othercountries besides the United States.

A “second level” of arsenic is a concentration within an aqueous mediumlower than the “first level.” Preferably the second level is aconcentration within an aqueous medium lower than the MCL. A “thirdlevel” of arsenic is a concentration within an aqueous medium lower thanthe second level. Preferably, this third level is a concentration lowerthan the MCL. As such, the first level is higher than the second level,which is higher than the third level. It is also envisioned thatadditional levels exist below the third level, each of which has anincrementally smaller amount of arsenic in the aqueous medium and eachof which is the result of contact with an additional amount ofchemically treated zeolite.

The arsenic removal systems and methods of the present invention aredesigned to be incorporated into conventional water treatment systems,and preferably are designed to be incorporated into these systems asstand-alone units. Typically, the incorporation of the systems andmethods of the present invention do not require that the existing systembe re-designed, but rather, that the arsenic removal systems and methodsbe adapted to function before, during or after the more conventionalwater treatment. Preferably, embodiments of the arsenic removal systemsand methods of the present invention are added to existing watertreatment facilities as a first treatment step. Preferably, embodimentsof the present invention remove an amount of arsenic from a water sourceto meet the MCL for arsenic in the United States, i.e., below 10 ppb.

The systems and methods of the present invention are adapted for usewith existing water treatment plants as a “turn-key” or “bolt-on”process to remove arsenic from aqueous media. These facilities can beused to improve the quality of aqueous media in a number ofapplications, including drinking water, waste water, agricultural waterand ground water. In the same manner, the systems and methods of thepresent invention can be incorporated into new water treatment plantdesigns, again as “turn-key” or “bolt-on” process to the conventionalwater treatment facility, or integrated into the facility as designed byone of skill in the art.

The reactions believed to take place in both the loading of the zeolite,for example with ferric ions, and the subsequent absorption of arsenicin the form of arsenate, from an aqueous medium are illustrated asfollows:Na⁺Zeol+Fe³⁺→Fe³⁺Zeol+3Na⁺Fe³⁺Zeol+AlO₄ ³⁻→(Fe³⁺AsO₄)Zeol

Of particular interest in this case is the fact that the resulting spentzeolite ((Fe³⁺AsO₄)Zeol) is insoluble. The insoluble spent zeolitepasses the EPA's Toxicity Characteristic Leaching Procedure (TCLP),allowing the spent zeolites to be disposed of at arsenic approvedlandfills or other like waste disposal facilities.

Referring to FIG. 1, a flow diagram of a method 100 for the removal ofarsenic from aqueous media is shown. In step 102, the level of arsenicis measured in the aqueous media feed to determine a first level ofarsenic. In step 104, an optional determination can be made as towhether the feed has sufficient arsenic content to require removal ofsome or all of the arsenic from the aqueous media. In cases where thefeed has an arsenic content below a target threshold of arsenic, themedium is passed directly to the conventional water treatment facility.In cases where the feed requires the removal of arsenic, the feed isdirected to treatment as shown by step 106. In step 106, the aqueousmedia is placed in contact with a sufficient amount of chemicallytreated zeolite for a sufficient amount of time to remove an amount ofarsenic so that the aqueous media has a second level of arsenic. Thisstep can be repeated so that the aqueous medium having a second level ofarsenic is contacted with a second amount of chemically treated zeoliteto remove an amount of arsenic, thereby leaving the aqueous media with athird level of arsenic. In each case the third level of arsenic is lowerthan the second level of arsenic which is lower than the first level ofarsenic.

In step 108, the treated aqueous media is discharged from the chemicallytreated zeolite and the level of arsenic is measured, this is thedischarge level of arsenic in the aqueous media. In step 110, apotential period of time, number of bed volumes, or other measuringprocess is used to determine the capacity of the chemically treatedzeolite under the conditions of the arsenic removal process. In step112, a determination is made in light of step 110 as to whether thechemically treated zeolite is sufficiently laden with arsenic to requirereplacement of the spent zeolite with fresh chemically treated zeolite.The spent zeolite is disposed of at the appropriate licensed arsenicapproved landfill. In preferred aspects of the methods of the presentinvention, the spent zeolite is replace before the arsenic capacity ofthe chemically treated zeolite is reached.

Referring to FIG. 2, a flow diagram of another method 200 for theremoval of arsenic from aqueous media is shown (note that steps 202, 204and 206 are interchangeable in relation to each other). In step 202, thelevel of arsenic is measured in the aqueous media feed to determine afirst level of arsenic. In steps 204 and 206, a determination is made asto the aqueous media flow and/or total volume of aqueous media to betreated by the chemically treated zeolite of the present invention, aswell as a determination as to the amount and capacity of chemicallytreated zeolite required to treat the aqueous media to reach apre-determined discharge level of arsenic. In preferred embodiments, thedetermination steps 204 and 206 are made so that the second or third ordischarge level of arsenic is slightly below a threshold value, forexample the MCL for arsenic in drinking water. Note that these stepsinclude a determination of whether to bypass the chemically treatedzeolite contact step (step 208) with a portion of the aqueous media atthe first level of arsenic. This allows for a mixing of a portion ofaqueous media at a first level of arsenic with treated aqueous mediahaving an arsenic content at a second level, providing the dischargelevel of arsenic. In step 208, the determined flow of aqueous media isplaced in contact with the determined amount of chemically treatedzeolite for a sufficient amount of time, and within a pre-specifiedrange of pH, to remove a predetermined amount of arsenic, preferably sothat the arsenic is present in the discharge at levels below a targetthreshold, for example the MCL for arsenic in the United States. In step210, the discharge level of arsenic in the aqueous media is measured andis preferably compared to the first and second levels of arsenic in theaqueous media.

In step 212, a portion of the spent zeolite is bled away from theaqueous media and replaced with an equal amount of fresh chemicallytreated zeolite. In step 214, the spent zeolite is disposed of in anarsenic approved landfill. In some cases, where the spent zeolite has anappropriate capacity for arsenic remaining, the zeolite can be reused inthe treatment of aqueous media, and is added to the chemically treatedzeolite in step 212, replacing fresh zeolite.

Referring to FIG. 3, a schematic showing a system 300 for removingarsenic from an aqueous medium is provided, the system having a housingmember, i.e., an absorption column or tank 302, charged with achemically treated zeolite. The housing member 302 containing thechemically treated zeolite can be operated as fixed or fluidized bed, oras a stirred reactor. The system also includes an arsenic monitoringdevice 304 to determine the arsenic levels at the feed 306 and a secondarsenic monitoring device 304 for determining the arsenic levels at thedischarge 308.

In use, the system 300 shown in FIG. 3 allows for the contact of thefeed 306, having a first level of arsenic, with the chemically treatedzeolite. The contacting step can be accomplished in a number of ways,including by a batch process, in which the aqueous medium is added tothe column, agitated and removed, or in a continuous manner, where theaqueous medium is fed to the column inlet and allowed to pass throughthe column (up-flow or down-flow). Preferably, the aqueous medium iscontacted with the chemically treated zeolite in an up-flow manner.

During the contact between the aqueous medium and the chemically treatedzeolite, arsenic is absorbed to the chemically treated zeolite therebydecreasing the concentration of the arsenic in the discharged aqueousmedium to a second level.

It should be noted that from an economic standpoint, it is desirable toremove only enough arsenic to keep the concentration of arsenic in theaqueous medium at the discharge just below a threshold level, forexample the MCL for arsenic. The discharge level is preferably measuredat a point in time when the aqueous medium is discharged from the systemfor further treatment by other processes. Adjustment of the dischargelevel of arsenic may be accomplished by adjusting the flow rate of theaqueous medium flowing through the tank, or the amount of chemicallytreated zeolite in the column to increase or decrease retention time.Additionally, an amount of aqueous medium containing arsenic at a firstlevel may be diverted from passing through the housing member andblended with the aqueous medium exiting the housing member. This allowsfor an alternative method of adjusting the second level of arsenic inthe aqueous medium. Further methods for adjusting the discharge level ofarsenic involve the use of a continuous bleed of the chemically treatedzeolite from the housing member, where an amount of chemically treatedzeolite is replaced in the absorption column(s) on a regular basis.e.g., once a day, with fresh or partially loaded (with arsenic)chemically treated zeolite. Finally, the adjustment of the dischargelevel of arsenic can be accomplished by varying the amount of chemicallytreated zeolite present in the housing member(s). The amount ofchemically treated zeolite used in the contact with the aqueous mediumdetermines, in part, the capacity of the system. As such, the morechemically treated zeolite in the system, the greater will be thepotential amount of arsenic that can be removed from the aqueous mediumand conversely, the smaller the amount of chemically treated zeolite inthe system, the smaller will be the potential amount of arsenic that canbe removed from the aqueous medium.

With continued reference to FIG. 3, the aqueous medium can bere-circulated over the chemically treated zeolite in the housing memberwhen the second level of arsenic is above a pre-determined thresholdvalue (see dashed line 310). The aqueous medium can be re-circulatedover the chemically treated zeolite, until the level of arsenic in theaqueous medium is appropriate for discharge from the system.

Referring again to FIG. 3, once the chemically treated zeolite is spent,or nearly spent, it is removed from the housing member and disposed ofin an approved landfill 312. For purposes of the present invention,zeolite is spent when it is no longer effective in absorbing arsenicfrom the aqueous medium to an adequate level. Preferably, spent zeoliteis removed from the housing member by means of vacuum suction, or otherlike procedures.

A determination as to whether chemically treated zeolite is spent ismonitored by selecting a particular threshold level of arsenic, forexample the MCL for arsenic, and monitoring the level that exits thechemically treated zeolite. It is also noted, that monitoring of thelevel of arsenic loaded onto the chemically treated zeolite isaccomplished by estimating the number of bed volumes required to achievea desired reduction in concentration of arsenic from the aqueous mediumand measuring the flow of the aqueous medium through the chemicallytreated zeolite. The estimation is based on an analysis of theparticular aqueous medium composition, the chemically treated zeoliteabsorption properties, the desired reduction of arsenic concentration inthe discharge, the anticipated flow rate, the housing member size andthe water treatment facility capacity.

Again with regard to FIG. 3, for example, the aqueous medium would bemonitored until a second level of arsenic exits the housing member, orby monitoring the flow rate through the housing member. Once the secondlevel of the aqueous medium exceeds the MCL, or the anticipated numberof bed volumes is reached, breakthrough occurs.

Another embodiment of the present invention is shown in FIGS. 4 and 5.In FIG. 4A, a schematic showing system 400 having a pair of housingmembers 402, for example columns, having appropriate amounts ofchemically treated zeolite, are placed in series for the removal ofarsenic from an aqueous medium. The system 400 further includes a firstarsenic monitoring device 404 for determining the first level ofarsenic, and a second arsenic monitoring device 406 for determining thethird level of arsenic or discharge level of arsenic. An additionalarsenic monitoring device 408 can be included for determining the secondlevel of arsenic, or the level of arsenic in the aqueous medium beforeit enters the second housing member, if needed.

In use, the aqueous medium having a first level of arsenic 410 entersthe first housing member and contacts the first amount of chemicallytreated zeolite. The aqueous medium exits the first housing memberhaving a second level of arsenic 412. The aqueous medium having a secondlevel of arsenic enters the second housing member and contacts thesecond amount of chemically treated zeolite. The aqueous medium exitsthe second housing member having a third level of arsenic 414. In thisembodiment, the third level of arsenic is also the discharge level ofarsenic. It is envisioned that additional columns can be added to thesystem where necessary. Also note that the aqueous medium can bere-circulated over the first or second amount of chemically treatedzeolite to achieve an additional decrease in the level of arsenic in theaqueous medium (see above) (dashed line 416).

Once the chemically treated zeolite in the first housing member isspent, the chemically treated zeolite is removed and fresh chemicallytreated zeolite added. This can be accomplished by physically replacingthe first housing member with a new housing member, where the newhousing member is charged with a pre-determined amount of chemicallytreated zeolite. The second housing member is moved in series to receivethe first level of arsenic and the new housing member is placed inseries to receive the aqueous medium containing the second level ofarsenic (see FIG. 5). In this way the chemically treated zeolite issystematically moved from the second housing member in the series to thefirst member in the series to removal from or out of the series 420. Inan alternative embodiment, the chemically treated zeolite is replacedwithout replacing the housing member itself. Here the flow of theaqueous medium having a first level of arsenic is switched to entirelygo through the appropriate housing member while the other housing memberhas its spent chemically treated zeolite replaced with new chemicallytreated zeolite (see FIG. 4B). Also note, as shown in FIG. 4B, thedesign of the flow through the housing members may be altered to run inparallel. In this embodiment, once the chemically treated zeolite isspent, the flow is diverted to re-circulate through one of the twohousing members, and the other housing member's spent material replacedwith fresh chemically treated zeolite. Once completed the flow isdiverted to the newly charged housing member and the chemically treatedzeolite in other housing member can be replace if appropriate. The flowof aqueous medium, as shown in FIG. 4B, can be appropriately directed inthe system by a series of valves 418, or other like devices.

It is envisioned that embodiments of the present invention could includeadditional housing members charged with chemically treated zeolitedepending on the needs of the system, and any number of differentcombinations of in-series and in-parallel or mixtures of in-series andin-parallel designs are within the scope of the present invention.

In general, one million gallons a day of water can be treated throughtwo 12×12 columns, each containing 8 to 9 feet of zeolite (see examplesbelow).

The embodiments of the present invention provide for the disposal ofspent chemically treated zeolite without the need to shut down the watertreatment facility, and provides redundancy for the system should anyone of the housing members fail for reasons such as bio-fouling,short-circuiting, leakage, or other potential mechanical difficulties.

Systems For Monitoring and Disposing of Arsenic From An Aqueous Medium

The present invention contemplates a system for operating the equipmentrequired to remove arsenic from a target water source by an off-siteprovider, for example a company that specifically installs, monitors,trouble-shoots, and disposes of the zeolite materials in thetanks/columns of the present invention. The off-site provider iscontemplated to be hired by a municipality or other like agency or groupto maintain the arsenic levels in the municipalities water via thesystems and methods of the present invention. The off-site provider isresponsible for determining the arsenic removal requirements of thetarget water source, for example a water treatment facility, includingthe type and amount of chemically treated zeolite required, the numberof tanks necessary to house the chemically treated zeolite, the designof the flow through the tanks, i.e., up-flow, down-flow or batch, andin-series or in-parallel, the flow rate of the aqueous medium, thelength of time or bed volumes before disposal, and the spent zeolitedisposal site. Note that other parameters may be involved in theoperation of the arsenic removal system that could be handled by theoff-site provided, such that the above list is meant for illustrativepurposes. The off-site provider provides the benefit of maintenance freeuse of the arsenic removal technology to the water treatment facilitymanager without having the burden of maintaining, monitoring, replacing,refreshing, or disposing of the loaded zeolite material(s). This systemprovides a financial benefit to the municipality or other water rightsholder, in that it allows the municipality to hire an arsenic removalspecialist to efficiently remove and dispose of arsenic to levels thatcomply with the EPA.

The off-site provider installs the properly charged chemically treatedzeolite materials at the water treatment facility and monitors the firstlevel, second level, discharge level, etc of the arsenic in the water.The arsenic monitoring can be technician based, i.e., a technician goesto the installed system and takes samples from the feed and dischargefor arsenic testing, or can be performed by a pre-programmed flowreading system that transmits, via wireless communication for example,the number of bed volumes or time elapsed that the system has been inuse, and whether the estimated capacity of the chemically treatedzeolite has been attained, to a off-site computer of other likeinstrument (the data can also be tabulated or graphed to establishtrends and other useful information). The off-site monitoring unit canbe equipped with a signaling means for alerting the off-site provider ofover target times or bed volumes, or can be equipped to read sensors inthe housing members or connection lines between housing members thatalert the off-site provider of potential problems in flow-rate,pressure, etc. In one embodiment, the off-site provider has thecapability of diverting the water supply from one source of chemicallytreated zeolite to a second source of chemically treated zeolite, whenthe provider receives a signal that the first source of chemicallytreated zeolite has contacted a pre-set threshold amount of aqueousmedium or been in use for a pre-set amount of time. Preferably, thediversion can be accomplished from an off-location site via wirelesssignal transmission.

The off-site provider is responsible for coordinating any maintenance ortroubleshooting issues that arise during the arsenic removal process. Assuch, alarms or other signaling devices may be included in the zeolitehousing members to alert the provider of a potential malfunction in thesystem. Further, the off-site provider is responsible for thereplacement and disposal of used or spent chemically treated zeolite,and in particular is responsible for the disposal of the spentchemically treated zeolite at approved arsenic disposal landfills.

This system if made possible by the simplicity of implementation,operation, monitoring, and servicing of the present invention. Asdescribed previously, the above-systems operate with housing members,for example columns charged with appropriate materials, which are easilybuilt, maintained, and serviced. Several columns can be usedin-parallel, or in-series, and any one of the columns can be replaced orshifted as desired, all with minimal interruption of the removal ofarsenic from the process flow. These processes, as noted above, can beperformed in an automated fashion from an off-site location. Thus, thetechnology could include a service structure wherein a column, aplurality of columns in parallel, a series of columns, or anycombination thereof, is serviced (replaced or refreshed) by a separateentity than that which owns or operates the water treatment facility. Inanother embodiment the off-site provider simply manages the oversight ofthe arsenic removal and disposal system, either through its own know-howor by hiring and maintaining specialized service personnel orindependent contractors.

Having generally described the invention, the same will be more readilyunderstood by reference to the following examples, which are provided byway of illustration and are not intended as limiting.

EXAMPLES

Note that the arsenic assay procedures used throughout the Examplessection were performed by the Commercial Testing & Engineering lab(CT&E) at 4665 Paris St., Denver, Colo. Analysis were performed usinggraphite furnace atomic absorption (GFAA) according to EPA protocolnumber 7000. Iron, calcium, sodium, etc concentrations were alldetermine using standard atomic absorption techniques known in the art.These procedures were in accordance with EPA protocol number 6010.

Also note that the chemically treated zeolites shown in the Examplesbelow were generally prepared according to the following protocol:

For laboratory scale experiments 500 grams of zeolite are placed in afour to eight liter container, and the container filled with water andstirred with a mechanical mixer for approximately thirty minutes. Thezeolite was allowed to settle and the water (generally containingsuspended clays and fines) decanted. Water was added to the settledsolids, remixed, and decanted an additional one or two times. Thesettled solids are dried at low temperature (35° to 50° C.) and sievedon a 35- or 40-mesh screen to remove any remaining fines. On a largerscale, the clays and fines are removed from the zeolite using commercialscrubbing, and sizing devices such as trommels, classifiers, andvibrating screens.

To absorb the appropriate metal ion onto the zeolite, for laboratoryscale experiments, 400 grams of dry, sieved zeolite are placed in a onegallon bottle with one hundred and fifty grams of commercial ferricsulfate and 3,500 ml water. The 150 grams ferric sulfate makes availableapproximately 2 milliequivalents (meq) ferric iron per gram of zeolite.A milliequivalent is defined as the amount of any element that willdisplace one milligram of hydrogen. It is in effect, a mass measurementadjusted for the electrical charge of the particular element.

The one gallon bottle is sealed and agitated on a roller apparatus forup to sixteen hours. Contact can also be accomplished using a one-galloncontainer and a mechanical stirrer, or other like technique. Once theferric iron is loaded onto the zeolite, the ferric-loaded zeolite can bedewatered and any generated fines removed on a 35- or 40-mesh sieve. Thedewatered zeolite is low-temperature dried, i.e., room temperature to50° C. Note that on a larger scale, a column is loaded with the sievedzeolite and ferric sulfate solution circulated through the column for apre-set number of bed volumes/time. After the zeolite is loaded with theferric ions, the solution is drained from the column, the zeoliteneutralized and rinsed, removed from the column and, if desired, lowtemperature dried. Other metal ions or mixtures of metal ions can beabsorbed onto the zeolite by providing in the contact solutionapproximately 2 meq of metal ion per gram zeolite.

Note also that the pH of the metal ion-zeolite contact is preferablymaintained between 2.0 and 2.5, requiring that the neutralization andrinse steps bring the pH up to approximately 4 to 5.5. This is typicallydone in a slow and controlled manner with the addition of NaOH or CaOHor other like base material.

Example 1 Preparation of Ferric-Loaded Zeolite

The data shown in FIG. 6, illustrates one embodiment for preparing achemically treated zeolite in accordance with the present invention.Three thousand pounds of ferric form zeolite was prepared by chargingtwo, 24 inch diameter columns each with 1500 pounds of 8×40 meshzeolite. Two hundred fifty pounds commercial ferric sulfate (0.9 meq/gzeolite) was dissolved in 4700 pounds water (560 gallons) and circulatedup-flow through the columns for 48 hours. After 48 hours, the solutioncontaining 3.5 g/L iron at 2.25 pH was drained from the columns anddiscarded. Approximately 0.6 meq Fe/gram was loaded onto the zeolite.

A second volume of solution was prepared by dissolving 390 poundscommercial ferric sulfate (1.4 meq Fe/g zeolite) in 4700 pounds water.This solution was circulated through the columns for approximately 48hours. The solution pH of 1.8 was raised to 2.1 by the addition ofsodium hydroxide. After 48 hours the solution containing 1.1 g/L iron at2.06 pH was drained from the columns and discarded. An additional 0.5meq Fe/g was loaded on the zeolite (total loading of 1.1 meq Fe/g).

The column was then rinsed with water to remove the residual, solubleiron. A final volume of water was circulated through the columns. Sodiumhydroxide was slowly added to the circulating solution until the pH wasgreater than 4.

The neutralization solution was drained from the column and the zeoliteremoved. The present Example illustrates the utility of the presentinvention for preparing a ferric-loaded zeolite for use in removingarsenic from an aqueous medium.

Example 2 Ferric-Loaded Zeolite Removes Arsenic With High Capacity

The data shown in FIGS. 7A-7C, were obtained by running the followingfixed column test:

A series of two, 250 ml burets, were set-up in series, where each buretcontained approximately 200 ml of ferric-loaded zeolite. Note that asmall wad of glass wool was inserted into the bottom of each buret priorto the addition of the ferric-loaded zeolite. A solution reservoir wasconnected to the bottom of the first buret using a Masterflex pump.

A solution containing 10 gallons of tap water, 0.16 grams sodiumarsenate (dibasic, heptahydrate), and 7.4 grams calcium chloride wasprepared. The solution was pumped slowly up-flow through theferric-loaded zeolite and collected at discharge for analysis. Dischargewas analyzed for arsenic levels.

The data illustrated in FIG. 7, show that ferric-loaded zeolites areextremely effective in removing arsenic from aqueous medium. FIG. 7Crepresents the performance of the first “column”—note that the twocolumns used in the Example are in series. Again with regard to FIG. 7,the concentration of arsenic (in the form of arsenate) in an aqueousmedium containing approximately 120 micrograms of arsenic per liter ofaqueous medium (equivalent to 120 ppb) is effectively reduced to lessthan 10 ppb for about 1715 bed volumes. In other words, breakthrough didnot occur for more than 1715 bed volumes.

Example 3 Other metal Ions Load Effectively Onto Zeolite

Preparation of loaded-zeolite materials was as described previously(above), except, that 50 grams of zeolite was contacted overnight in abeaker having water solutions as shown in Table 4. Each solution wasmechanically stirred for a period of from 1 to 16 hours.

TABLE 4 Arsenic Absorption Using Barium,, Aluminum, Calcium, Ferric AndFerrous-Loaded Zeolites Purpose: Evaluate Ba, Al, Ca, Fe++, and Fe+++forms of zeolite for arsenic removal from water Procedure: Contact 50gram portions of zeolite overnight in water solutions of the above toconvert them to the respective forms. Add 2 meq/gram 1 Use 12.2 gramsBaC12.2H2O in 500 ml water 2 Use 11.1 grams A12(SO4)3.18H2O in 500 mlwater 3 Use 11.8 grams CaNO3.4H2O in 500 ml water 4 Use 13.9 gramsFeSO4.7H2O in 500 ml water 5 Use 9.4 grams Fe2(SO4)3.xH2O in 500 mlwater Sieve solutions to recover zeolite and rinse zeolite with water.Discard solutions. Contact each zeolite aliquot overnight with 3 litersdemineralized water containing 100 ppb arsenic as sodium arsenate 6.7milligrams Na2HasO4.7H2O in 16 liters water Take 1 liter water as headsample - 5-7-0 Sieve solutions to recover zeolite. Submit solutions forarsenic. Loaded onto Zeolite As, μg/l Removal, % meq/g g/kg Label: 5-7-095 5-7-1 85 11% 0.00004 0.0006 5-7-2  5 95% 0.00036 0.0054 5-7-3 86  9%0.00004 0.0005 5-7-4 25 74% 0.00028 0.0042 5-7-5 <5 >95%  0.00036 0.0054Note: Calculation assumes 75/5 as equivalent weight of arsenic

The data in Table 4 shows that a solution containing 100 ppb of arsenicas sodium arsenate, contacted with various chemically treated zeolites(including barium-loaded zeolite, aluminum-loaded zeolite, andferric-loaded zeolite) resulted in the removal of an amount of arsenicfrom solution. For example, the barium-loaded zeolite removedapproximately 11% of the arsenic, the aluminum-loaded zeolite removedapproximately 95% of the arsenic and the ferric-loaded zeolite removedgreater than 95% of the arsenic.

Example 4 Ferric-Loaded Zeolite is Effective At Removing Arsenite FromAqueous Medium

Five grams of ferric-loaded zeolite (prepared as described above) wascontacted with 300 ml of demineralized water containing 300 ppb arsenicas sodium arsenite. Table 5 shows that approximately 75% of the arsenicin the form of arsenite is removed from the starting material.

TABLE 5 Removal Of Arsenic Using Ferric-Loaded Zeolites Purpose:Evaluate Fe+++ forms of zeolite for arsenite removal from water.Procedure: Contact 5 grams zeolite overnight with 300 millilitersdemineralized water containing 300 ppb arsenic as sodium arsenite 0.3milligrams NaAsO2 in 500 milliliters water As, ppb Take 200 ml balanceas head sample - 6-5-0 538 Submit final filtrate as 6-5-1 134 Loaded onto zeolite meq As(3)/g 0.0006 g/kg 0.016 Removal 75% Note: Calculationassumes 75/3 as equivalent weight of arsenic

The example illustrates the utility of using the present invention forremoving arsenite from an aqueous medium.

Example 5 Ferric Hydroxide-Loaded Zeolite is Effective At RemovingArsenate From Aqueous Medium

The ferric-hydroxide-loaded zeolite was prepared as describedpreviously. A 250-ml buret was charged with 200 ml of the ferrichydroxide loaded-zeolite for this particular Example.

The tabular data in FIGS. 8A and 8B shows that ferric hydroxide-loadedzeolite is effective in removing arsenic in the form of arsenate tolevels below 20 ppb, having a capacity of approximately 1,300 bedvolumes. The Example illustrates the utility of using ferrichydroxide-loaded zeolite for the removal of arsenate from an aqueousmedium.

Example 6 Activated Alumina-Loaded Zeolite is Effective At RemovingArsenate From Aqueous Medium

A standard test solution of arsenic was prepared by combining one litertap water with 1.575 grams sodium arsenate and 0.7 grams calciumchloride (the solution contained 385 mg arsenic/L). A ferric-loaded andactivated alumina-loaded zeolite column was prepared as previouslydescribed. Note that the calcium chloride was added to simulatepotentially high levels of calcium found in drinking water.

One hundred ml of the arsenic solution was contacted with varyingamounts of either ferric-loaded zeolite or activated alumina-loadedzeolite in a flask for a period of 12 hours. As shown in Table 6, theferric-loaded zeolite absorbed 6 grams of arsenic/kg, while theactivated-alumina-loaded zeolite absorbed over 36.5 grams of arsenic/kg.This Example again shows the utility of the present invention forproviding a high capacity arsenic removal system, the system can utilizeseveral different loaded zeolites.

TABLE 4 Test To Determine Maximum Loading Of Arsenic On Ferric-LoadedZeolite And Activated Alumina Purpose: To determine maximum arsenicloading onto zeolite Procedure: Prepare 1 liter of arsenic solution Makeup water for treatment. Pe 1 Liter 1.575 grams sodium arsenate (dibasic,heptahydrate) 0.7 grams calcium chloride (anhydrous) Loaded. Arsenic As,ms/l meq/g g/kg Contact 100 mL arsenic solution with 385 1) 1 gramferric form zeolite 325 0.400 6.0 2) 2 gram ferric form zeolite 2600.417 6.3 3) 4 gram ferric form zeolite 145 0.400 6.0 4) 8 gram ferricform zeolite 20 0.304 4.6 submit solutions for analysis 5) 1 gramAAFS-50 20 2.433 36.5 6) 2 gram AAFS-50 40 1.150 17.3 7) 4 gram AAFS-50<3 0.637 9.6 8) 8 gram AAFS-50 <3 0.318 4.8 Note: Calculation assumes75/5 as equivalent weight of arsenic

Example 7 Industrial Scale Removal of Arsenic From an Aqueous Medium

The amount of chemically treated zeolite required for a particular use,and the size of the tank for commercial applications, are selected basedon numerous parameters, including, but not limited to, average amount oftrace elements in the aqueous medium, desired levels of reduction inarsenic, the water treatment facility size/capacity, and the type ofchemically treated zeolite in use.

Predictable scale-up for the methods according to the present inventionwill be described in detail with respect to several parameters based onexperimental data as described above and applied to a theoretical onemillion gallon per day (MGD) treatment facility. The aqueous mediumcontained an average of 20 ppb arsenic as arsenate and the desiredreduction in concentration is to 10 ppb arsenic. The design flow rate ofthe tank is approximately 6 gal/ft². The zeolite is 20×40 meshclinoptilolite.

Table 7 summarizes a typical scale-up calculation for an industrialsized system. As shown in the Table, removal of 5 ppb arsenic requires189 kg zeolite per day or 69 tons of zeolite per year. At a flow rate of694 gallons/min the effective tank size will be approximately 12 feet indiameter and at least 12 feet in height. A system designed to thesespecifications will require replacement of the tank and/or zeolite every187 days (about every 6 months).

TABLE 5 Arsenic Design Analysis Delta arsenic recovered 15 umg/lAssumption umg arsenic/gallon 56.7 umg/gallon Gallons/day 1,000,000gallons Assumption Liters/day 3,785,000 liters Zeolite capacity 300 mgAs/kg zeolite Assumption mg arsenic/day recovered 56,775 mg arsenic/daykilos zeolite loaded 189 kilos per day kilos per year for disposal69,076 kilos Tons per year for disposal 69 tons Design flow rate of tank6 gal./sq. ft. Assumption Flow rate of water to be 694 gpm treated Areaneeded 116 sq. ft. Diameter of tanks 12 feet kilos of zeolite per 25kilos cubic foot kilos of zeolite per 1 2894 kilos foot depth days perfoot of zeolite 15 days in tank Velocity in tank 0.80 ft/minute EBCTneeded 15 min. Assumption Depth of zeolite needed 12 ft Tank Life 187days

Example 8 Pilot Studies On Arsenic Removal Using 4 or 10 ColumnIn-Series Systems

The systems and methods of the present invention were used in two pilotstudies to treat 104,000 gallons (FIG. 9A) or 66,000 gallons (FIG. 9B)water. Water at the Meyers-Track, Pa., site was run through a series of10 in-series 6″×8′ sized columns each containing 5′ of chemicallytreated zeolite, until a total of 104,812 gallons of water were treated.Arsenic levels were followed, and graphed. Note that the 10 columnsystem removed arsenic from a feed level of arsenic in violation of the10 ppb EPA arsenic level to discharge levels in the 2.5 ppb levels.

FIG. 9B illustrates a 4 column pilot study at Bernalilla, N. M., eachcolumn being 6″×8′ in size and containing 8′ of zeolite, to treat 66,000gallons of water, where feed levels of arsenic were around 0.01 mg/L anddischarge levels lowered to 0.002 mg/L.

The present Example again illustrates the utility of the presentinvention for removing arsenic from an aqueous medium, especially inlight of the natural aqueous medium sources.

It should be understood for purposes of this disclosure, that variouschanges and modifications may be made to the invention that are wellwithin the scope of the invention. Numerous other changes may be madewhich will readily suggest themselves to those skilled in the art andwhich are encompassed in the spirit of the invention disclosed hereinand as defined in the appended claims.

1. A system for removing arsenic from a water source, the system in-linewith a water treatment facility, the system comprising: a predeterminedamount of ferric-loaded zeolite for absorbing arsenic from apredetermined volume from the water source; and a housing member forconstraining the predetermined amount of ferric-loaded zeolite forcontact with the water source, the housing operatively connected to thewater treatment facility; wherein, the water source has a first level ofarsenic before it contacts the predetermined amount of ferric-loadedzeolite and a second level of arsenic after it contacts thepredetermined amount of ferric-loaded zeolite, the second level ofarsenic lower than the first level of arsenic in the water source andwherein at least some of the water from the water source will be used aspotable water; a second predetermined amount of ferric-loaded zeolitefor absorbing arsenic from the water source after the water source hascontacted the first predetermined amount of ferric-loaded zeolite; and asecond housing for constraining the second predetermined amount offerric-loaded zeolite for contact with the water source; wherein, thewater source has a third level of arsenic after it contacts the secondamount of chemically treated zeolite, the third level of arsenic lowerthan the second level of arsenic in the water source; and apredetermined amount of aluminum-loaded zeolite, mixed with the ferricloaded zeolite, for absorbing arsenic from the water source.
 2. Thesystem of claim 1 further comprising: a flow meter for tracking thevolume water source to contact the predetermined amount of ferric-loadedzeolite, wherein a threshold volume has been predetermined to representthe capacity of the predetermined amount of ferric-loaded zeolite. 3.The system of claim 2 further comprising a system manager fordetermining replacement and disposal of the predetermined amount offerric-loaded zeolite, the system manager located at least partiallyoff-site from the system and water source.
 4. The system of claim 3further comprising a signaling device for alerting the off-site systemmanager that a volume of water has been reached through thepredetermined amount of ferric-loaded zeolite.
 5. The system of claim 4wherein the signaling device wirelessly communicates to the off-sitesystem manager that a volume of water has been reached through thepredetermined amount of ferric-loaded zeolite.
 6. The system of claim 1wherein the housing member has a separate inlet for receiving the watersource and outlet for discharging the water source.
 7. The system ofclaim 1 further comprising a vacuum device for removing thepredetermined amount of ferric-loaded zeolite from the housing memberafter the predetermined amount of ferric-loaded zeolite has contactedthe water source over a period of time, wherein the removedferric-loaded zeolite is disposed of at an arsenic approved landfill.